The present invention disclosed herein relates to a display including a nano-scale LED and a method for manufacturing the same, and more particularly, to a display including a nano-scale LED in which a nano-scale LED device having a nano unit is connected to an electrode without an electrical short-circuit to realize a full-color LED display and maximize light extraction efficiency and a method for manufacturing the same.
The development of light emitting diodes (LEDs) has been actively promoted by succeeding in combination of a high-quality single-crystal gallium nitride (GaN) semiconductor by applying a low-temperature GaN compound buffer layer, by Nakamura et al., at Nichia Chemical Corporation in Japan, 1992. Such an LED is a semiconductor having a structure in which an n-type semiconductor crystal having a plurality of carriers, i.e., electrons and a p-type semiconductor crystal having a plurality of carrier, i.e., holes are junctioned to each other by using characteristics of a compound semiconductor, that is to say, a semiconductor device that converts an electrical signal into light having a desired wavelength band to emit the light. The LED semiconductor is called a revolution of light as a green material because the LED semiconductor has vary low energy consumption due to high light conversion efficiency and is semi-permanent in the lifespan and environmentally friendly. Recently, as development of compound semiconductor technologies, red, yellow, green, blue, and white LEDs having high luminance have been developed.
Thus, the development of LED lightings and LED displays using the LEDs are being continuously developed. Among these, since the LED displays are capable of being utilized as displays for small-sized electronic devices such as mobile phones and notebooks, studies on the LED displays are being actively carried out.
However, the LEDs are limitedly utilized for displays. For example, one of them may be a liquid crystal display (LCD). Since the LCD does not voluntarily generate light, a backlight for generating light has to be provided on a rear surface of a communication LED panel. White light is irradiated to the rear surface of the LCD panel to allow an image color realized by the LCD panel to be reproduced with approximation to an actual color. Although cold cathode fluorescent lamps (CCFLs) or external electrode fluorescent lamps (EEFLs) are initially used as light sources, after high efficiency light emission diodes (LEDs) having superior physical and chemical characteristics come, backlight using LEDs as light sources are being put to practical use. Furthermore, attempts to commercialize LEDs for full-color displays, but simple backlights are going on.
Particularly, due to these attempts, the current commercialized full-color LED displays have been produced as products that come in only contact with everyday lift such as displays for outdoor electronic display boards in which ten thousands to several hundred thousand of LED lamps having three primary colors, i.e., red, green, and blue colors are inserted into a large-scale board. In case of household TVs that are, so-call, called LED TVs or monitors for computers, the conventional fluorescent lamps are replaced with backlights having LED panel to LCD TVs or monitors in which white or three primary colors LED devices are adopted for backlights. Thus, the LCD TVs or motors are not LED displays in the true sense of the term.
A reason in which the existing LED devices are not developed as displays having the same size as TVs or monitors, there are fundamental limitations in technical methods for manufacturing displays and methods for realizing full colors by using the LED devices.
If a display for TVs is manufactured by using the existing LED devices, when simply calculated, about 5 to about 40 sheets of wafers, each of which has a width of about 2 inches to about 8 inches, have to be connected to each other to manufacture a TV having a width of about 40 inches. Thus, there are many limitations which are impassable through the present technologies in direct realizing of the display for the TV by using the LED devices through the presently well-known manufacturing technologies. Furthermore, to realize the full colors, since the red, green, and blue colors, i.e., three-primary color LED devices have to be inserted together into one pixel, it may be difficult to realize LED full-color displays by simply connecting red, green, and blue LED wafers to each other.
According to many studies that are known until now to realize high-efficiency LED displays, in case of a bottom-up method in which the group III-V thin films and nanorod LED devices are directly grown on a patterned pixel of a glass substrate having a large area for actual displays, it may be crystallographically very difficult to directly deposit the group III-V thin films on the large-scaled substrate having the same size as the displays for the TVs or grow the group III-V thin films having high crystalline and efficiency and the nanorod LED device on a patterned transparent electrode of the transparent amorphous glass substrate. Due to the technical limitation as described above, the method in which the LED devices are directly grown on the large-area glass substrate to realize the full-color display for the TVs or monitors is not nearly attempted.
The other method that proceeds by many researchers to realize the LED displays is a bottom-up method based on nano technologies. This method may be a method in which a nanorod LED is grown on a single crystal substrate and then portions of the grown nanorod LED are separated and rearranged on the electrode that is patterned by pixels by using the bottom-up method to realize the large-area display. However, the nanorod LED that is manufactured by using the bottom-up method may have a limitation in that light emitting efficiency is poor when compared to that of the existing thin film type LED that is grown on the wafer.
Further another method is a top-down method in which a high-efficiency LED device is cut to realize an LED display. In general, this method may be a method in which micro LED devices manufactured by using the top-down method are arranged one by one on sub pixels of the large-area glass substrate to one-to-one correspond to each other, thereby realizing the display. In this case, since an LED device is grown on a sapphire substrate and then patterned to a micro size to manufacture a micro LED device to be connected to the electrode, a micro LED display that has a size less than that of the wafer may be realized.
The above-described last method may be preferable in realizing of the LED display under the present technical level. However, in an electrode line of the manufactured LED device, if the other electrode is stacked by using the bottom-up method and then is three-dimensionally coupled to the electrode line, the LED device has to three-dimensionally stand up between the two electrodes different from each other and then is coupled to the two electrodes. This method may be possible in case of the general LED device. However, if the LED device is manufactured to a nano-scale LED device, it may be difficult to three-dimensionally stand up on the electrode, and thus, a portion of the electrode devices may be laid to cause pixel defects.
Also, even though the nano-scale LED device three-dimensionally stands up on the electrode, it may be difficult to one-to-one couple the LED devices to the nano-scale electrodes different from each other. Furthermore, even though the LED devices are one-to-one coupled to the two electrodes, it may be very difficult to electrically connect the LED devices to the two electrodes without causing electrical short-circuit. Although only one to two pixels are defective as described above, the whole display may be defective to cause defects of the display itself.
Korean Patent Application No. 2011-0040925 by the inventor of this application discloses a structure in which a nano-scale LED device three-dimensionally stands up and then is coupled to an electrode to realize a display device, and also, a structure in which a coupling link is disposed on a lower portion of the nano-scale LED device so that the nano-scale LED device easily and three-dimensionally stands up and is couple the LED device. However, in the actual realization of the display device, it may be very difficult to allow the nano-scale LED device to three-dimensionally stand up and be coupled to the electrode.
Also, if only one LED having a micro unit corresponds to each pixel, the defect of the LED may be regarded as a pixel defect.
Furthermore, since the sub pixel formed in the display is disposed on the electrode, even though the nano-scale LED having a nano unit three-dimensionally stands up and is coupled to the electrode, photons generated in an active layer of the nano-scale LED device may not be completely extracted although the photons are interdigitatedly disposed in a nano device and an insulation layer. Thus, light may be totally reflected by a surface formed between a surface of the standing LED device having the nano unit and an air layer to deteriorate light extraction efficiency. In addition, the photons may be blocked by the upper electrode and thus may not be extracted to the outside, but be absorbed into the active layer to deteriorate the light extraction efficiency.
Korean Patent Application No. 2006-0060461 discloses a light emitting diode display device and a method for manufacturing the same. In the disclosed light emitting diode display device, the display device constitutes one pixel and includes several LEDs. The LED is manufactured in the bottom-up method in which the nanorod LED device is directly grown. A reason in which this method is used in the foregoing invention is because it is difficult to allow the independently manufactured LED devices, i.e., several nano-scale LED devices, each of which has the nano unit, to three-dimensionally stand up and be coupled to the electrode.
However, according to the foregoing method, it may be substantially difficult to directly grow the LED devices on the large-area substrate.
Also, in case where the grown LED devices have sizes different from each other, it may be difficult to adjust density of the LED devices disposed on one pixel because the LED device is miniaturized to the nano size. Furthermore, it may be difficult to integrate the LED devices to high density, and since the electrode is disposed on each of upper and lower portions of the LED device, the photons generated in the LED device are totally reflected by a difference in refractive index and are not emitted to the outside due to the blocking of the electrode and thus captured or absorbed in the electrode layer. Thus, the deterioration in light extraction efficiency may not be solved.